A heat treatment method for improving corrosion resistance of 316L austenitic stainless steel

Abstract

The application discloses a heat treatment method for improving corrosion resistance of 316L austenitic stainless steel, which comprises the following steps: firstly, carrying out multi-pass cold rolling on the bright 316L austenitic stainless steel after surface treatment to a deformation of 75-85%; and then, carrying out annealing treatment on the 316L austenitic stainless steel after the multi-pass cold rolling in an argon protection or vacuum protection 750-780 DEG C annealing furnace to obtain a layered heterogeneous structure microstructure. The corrosion resistance of the obtained 316L austenitic stainless steel in liquid lead bismuth eutectic alloy is significantly improved. The safety of the 316L austenitic stainless steel cladding tube with the layered heterogeneous structure microstructure prepared by the method is improved in a lead-based reactor, the method has low cost and high operability, and can meet the corrosion resistance requirement of the cladding tube in the liquid lead bismuth eutectic alloy in the lead bismuth reactor.

Description

Technical Field

[0001] This invention belongs to the field of material heat treatment technology, specifically relating to a heat treatment method for improving the corrosion resistance of 316L austenitic stainless steel. Technical Background

[0002] Nuclear energy, with its advantages of environmental friendliness and sustainable development, has become one of the effective methods for addressing the global energy crisis and environmental problems. With the continuous development of reactors, fourth-generation reactors have become a global research hotspot due to their significant advantages in safety and economy. In lead-bismuth cooled fast reactors, the selection of core materials is crucial for the safe operation of nuclear power plants. Austenitic stainless steel, with its excellent machinability and corrosion resistance, is widely used as a reactor structural material. Among them, 316L austenitic stainless steel shows good potential in radiation resistance and corrosion resistance. Since liquid metal corrosion (LMC) in new-generation lead-based reactors poses a serious threat to the integrity and lifespan of the cladding material structure, a 316L austenitic stainless steel with improved resistance to lead-bismuth corrosion has been developed to enhance the lifespan of lead-bismuth cooled fast reactors and improve nuclear reactor safety. Summary of the Invention

[0003] This invention proposes a heat treatment method to improve the corrosion resistance of 316L austenitic stainless steel against liquid lead-bismuth eutectic alloys. The method is highly operable, low-cost, and simple. This invention enhances the corrosion resistance of 316L austenitic stainless steel through layered heterogeneous microstructure construction and heat treatment, resulting in 316L stainless steel with excellent corrosion resistance.

[0004] The technical solution of the present invention is as follows:

[0005] A heat treatment method to improve the corrosion resistance of 316L austenitic stainless steel to liquid lead-bismuth eutectic alloy:

[0006] S1: A 10mm thick bright 316L austenitic stainless steel with surface treatment was solution treated and held at 1050-1100℃ for 30min to obtain a uniform austenitic microstructure sample with an average grain size of 70-80μm.

[0007] S2: The S1 sample is subjected to multiple cold rolling processes until the total deformation reaches 85%;

[0008] S3: The samples processed in S2 are returned to the annealing furnace at 750-780℃ under argon or vacuum protection.

[0009] S4: The annealing time of the sample in S3 is 10-30 min to obtain a 316L austenitic stainless steel sample with a layered heterostructure.

[0010] S5: The sample obtained in S4 is encapsulated in the same quartz tube as lead-bismuth particles and placed in a box-type resistance furnace at 550°C to fully melt the lead-bismuth eutectic alloy and etch it at high temperature.

[0011] Preferably, the chemical composition of the 316L austenitic stainless steel in S1, by weight percentage, is: C: 0.024; Si: 0.32; Mn: 1.01; P: 0.024; S: 0.003; Cr: 16.43; Ni: 10.02; Mo: 2.04, with the balance being iron and other unavoidable impurity elements.

[0012] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0013] (1) The processing method of the present invention obtains austenite with uniform grain size through high temperature solid solution treatment.

[0014] (2) The treatment method of the present invention is more resistant to electrochemical corrosion of 3.5% NaCl aqueous solution than conventional 316L austenitic stainless steel.

[0015] (3) The processing method of the present invention is more resistant to high-temperature corrosion of liquid lead-bismuth eutectic alloy than conventional 316L austenitic stainless steel. Attached Figure Description

[0016] The accompanying drawings are used to illustrate specific embodiments of this experiment and form part of the application, but do not constitute a limitation on the embodiments of the present invention.

[0017] Figure 1 Electrochemical corrosion comparison between conventionally treated samples and samples treated according to the present invention: a is the heat-treated sample of Comparative Example 1, and b is the heat-treated sample of Example 1.

[0018] Figure 2 The images show a comparison of scanning electron microscope (SEM) images of conventionally treated samples and samples treated according to the present invention after being etched with liquid lead-bismuth eutectic alloy at 550°C for 250 hours: a is the heat-treated sample of Comparative Example 2, and b is the heat-treated sample of Example 2.

[0019] Figure 3 The images show a comparison of scanning electron microscope (SEM) images of conventionally treated samples and samples treated according to the present invention after being etched with liquid lead-bismuth eutectic alloy at 650°C for 250 hours: a is the heat-treated sample of Comparative Example 3, and b is the heat-treated sample of Example 3.

[0020] Figure 4 The corrosion depth of conventionally treated samples and samples treated according to the present invention after being corroded by liquid lead-bismuth eutectic alloy at 550°C for 250 hours is statistically analyzed: a is the heat-treated sample of Comparative Example 2, and b is the heat-treated sample of Example 2.

[0021] Specific Implementation Cases

[0022] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but the present invention is not limited to the following embodiments.

[0023] In this embodiment, the widely used 316L austenitic stainless steel is used as the research object. Its chemical composition by weight percentage is as follows: C: 0.024; Si: 0.32; Mn: 1.01; P: 0.024; S: 0.003; Cr: 16.43; Ni: 10.02; Mo: 2.04, with the balance being iron and other unavoidable impurity elements. The 316L austenitic stainless steel product used in this embodiment has a specification of 10*10*1.5mm.

[0024] Example 1

[0025] A heat treatment method to improve the resistance of 316L austenitic stainless steel to electrochemical corrosion by NaCl aqueous solution:

[0026] S1: Place the 316L austenitic stainless steel sample in a box-type resistance furnace nei1 and heat it to 190℃ (1050℃) on AC3 at a rate of 80℃ / min for a high-temperature solution treatment. After the alloying elements and most of the carbides in the sample are fully dissolved, hold the sample at the temperature for 30 minutes.

[0027] S2: Take out the heat-insulated sample, polish the surface, and then perform multiple cold rolling passes until the total deformation reaches 85%.

[0028] S3: Anneal the cold-rolled sample by holding it at 750℃ for 10 minutes.

[0029] S4: The sample was placed in NaCl solution for electrochemical corrosion, and the sample polarization curve was obtained as follows. Figure 1 .

[0030] Example 2

[0031] A heat treatment method to improve the corrosion resistance of 316L austenitic stainless steel to liquid lead-bismuth eutectic alloy:

[0032] S1: Place the 316L austenitic stainless steel sample in a box-type resistance furnace nei1 and heat it to 190℃ (1050℃) on AC3 at a rate of 80℃ / min. Perform a high-temperature solution treatment to obtain a uniform austenitic structure with an average grain size of 70-80μm. The holding time is 30min.

[0033] S2: Take out the heat-insulated sample, polish the surface, and then perform multiple cold rolling passes until the total deformation reaches 85%.

[0034] S3: Anneal the cold-rolled sample by holding it at 750°C for 10 minutes under argon or vacuum protection.

[0035] S4: The sample and lead-bismuth particles were packaged together in the same quartz tube and placed in a box-type resistance furnace at 550°C to fully melt the lead-bismuth eutectic alloy and then subjected to high-temperature corrosion with the sample for 250 hours.

[0036] Example 3

[0037] A heat treatment method to improve the corrosion resistance of 316L austenitic stainless steel to liquid lead-bismuth eutectic alloy:

[0038] S1: Place the 316L austenitic stainless steel sample in a box-type resistance furnace and heat it to 190℃ (1050℃) on AC3 at a rate of 80℃ / min. Perform a high-temperature solution treatment to obtain a uniform austenitic structure with an average grain size of 70-80μm. The holding time is 30min.

[0039] S2: Take out the heat-insulated sample, polish the surface, and then perform multiple cold rolling passes until the total deformation reaches 85%.

[0040] S3: Anneal the cold-rolled sample by holding it at 780°C for 15 minutes under argon or vacuum protection.

[0041] S4: The sample and lead-bismuth particles were packaged together in the same quartz tube and placed in a box-type resistance furnace at 650°C to fully melt the lead-bismuth eutectic alloy and then subjected to high-temperature corrosion with the sample for 250 hours.

[0042] Comparative Example 1

[0043] S1: Place 316L austenitic stainless steel in a box-type resistance furnace and heat it to 190℃ (1050℃) above AC3 at a rate of 80℃ / min for a high-temperature solution treatment. After the alloying elements and most of the carbides in the sample are fully dissolved, hold the temperature for 30 minutes.

[0044] S2: The sample was placed in NaCl solution for electrochemical corrosion, and the sample polarization curve was obtained as follows. Figure 1 .

[0045] Comparative Example 2

[0046] S1: Place 316L austenitic stainless steel in a box-type resistance furnace and heat it to 190℃ (1050℃) above AC3 at a rate of 80℃ / min for a high-temperature solution treatment. After the alloying elements and most of the carbides in the sample are fully dissolved, hold the temperature for 30 minutes.

[0047] S2: The sample and lead-bismuth particles are packaged together in the same quartz tube and placed in a box-type resistance furnace at 550°C to fully melt the lead-bismuth eutectic alloy and then subjected to high-temperature corrosion with the sample for 250 hours.

[0048] Comparative Example 3

[0049] S1: Place 316L austenitic stainless steel in a box-type resistance furnace and heat it to 190℃ (1050℃) above AC3 at a rate of 80℃ / min for a high-temperature solution treatment. After the alloying elements and most of the carbides in the sample are fully dissolved, hold the temperature for 30 minutes.

[0050] S2: The sample and lead-bismuth particles were packaged together in the same quartz tube and placed in a box-type resistance furnace at 650°C to fully melt the lead-bismuth eutectic alloy and then subjected to high-temperature corrosion with the sample for 250 hours.

[0051] Figure 1 The electrochemical corrosion comparison between conventionally treated samples and samples treated according to the present invention (a is the heat-treated sample of Comparative Example 1, b is the heat-treated sample of Example 1) shows that the breakdown potential of the heat-treated sample of Example 1 is significantly higher than that of the comparative sample, which proves that the heat-treated sample of Example 1 has excellent corrosion resistance.

[0052] Figure 2 The images show a comparison of scanning electron microscope (SEM) images of conventionally treated samples and samples treated according to the present invention after being etched with liquid lead-bismuth eutectic alloy at 550°C for 250 hours (a is the heat-treated sample of Comparative Example 2, b is the heat-treated sample of Example 2). It can be seen from the images that the thickness of the etched layer in the comparative example is greater than that in the heat-treated sample of Example 2.

[0053] Figure 3 The images show a comparison of scanning electron microscope (SEM) images of conventionally treated samples and samples treated according to the present invention after being etched with liquid lead-bismuth eutectic alloy at 650°C for 250 hours (a is the heat-treated sample of Comparative Example 3, b is the heat-treated sample of Example 3). It can be seen from the images that the thickness of the etched layer in the comparative example is greater than that in the heat-treated sample of Example 3.

[0054] Figure 4 To statistically analyze the corrosion depth of the lead-bismuth etched samples and the heat-treated samples (a is the heat-treated sample of Comparative Example 2, b is the heat-treated sample of Example 2), the statistical method was to etch the conventionally treated sample and the sample treated according to the present invention in a liquid lead-bismuth eutectic alloy at 550°C for 250 h, and then use a scanning electron microscope to measure the thickness of the corrosion layer on the sample cross-section. Corrosion layer thickness data was obtained at 2 μm intervals, and the average value of all obtained corrosion layer thickness data was compared. The corrosion layer thickness measurement showed that the corrosion layer depth of the Example sample was less than that of the Comparative Example sample.

[0055] Although the main inventive examples that influence the factors of this experiment have been described and listed, those skilled in the art will understand that various changes, explorations, modifications and combinations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A heat treatment method for improving the corrosion resistance of 316L austenitic stainless steel, characterized in that, The prepared 316L austenitic stainless steel improves the corrosion resistance of lead-bismuth eutectic alloys, specifically through the following steps: S1: Solution treatment is performed on 10mm thick bright 316L austenitic stainless steel at a temperature of 1050-1060℃ for 30 minutes. By holding the sample at 1050-1100℃ for 30 min, a uniform austenitic microstructure with an average grain size of 70-80 μm was obtained. S2: The S1 sample is subjected to multiple cold rolling processes until the total deformation reaches 85%; S3: Anneal the sample treated in S2 in an annealing furnace at 750-780℃; the annealing is carried out under argon protection or vacuum protection. S4: The annealing time of the sample in S3 is 10-30 min to obtain 316L austenitic stainless steel with a layered heterostructure; The chemical composition of the treated 316L austenitic stainless steel, by weight percentage, is as follows: C: 0.024%; Si: 0.32%; Mn: 1.01%; P: 0.024%; S: 0.003%; Cr: 16.43%; Ni: 10.02%; Mo: 2.04%, with the balance being iron and other unavoidable impurity elements.

Images